Photoelectric sensors are widely applied in detection and control due to the advantages of high precision, rapid response, non-contact, numerous measurable parameters, simple structure, etc. For example, the photoelectric sensor may be applied in the aspects of smoke and dust turbidity monitors, bar code scanning pens, product counters, photoelectric smoke alarms, rotation speed measuring instruments, laser weapons, etc.
The photoelectric sensor comprises an array substrate. The array substrate includes thin-film transistors (TFTs) and photodiodes. The photodiodes receive light and convert optical signals into electrical signals via photovoltaic effect, respectively control the storage and read of the electrical signals by switching off and on the TFTs, and hence achieve the function of detection or control. Thus, the performances of the TFTs are very important in the photoelectric sensor. Signal interference and light leakage are key factors for affecting the performances of the TFTs.
In order to obtain better signal-to-noise ratio (SNR), a signal shielding metal layer is usually additionally arranged on the TFTs of the photoelectrical sensor, and subsequently, a stabilized voltage is applied to the signal shielding metal layer to shield the induction current produced by electrical fields of sensing electrodes on source electrodes and drain electrodes, so that the influence on the performances of the TFTs can be reduced. But this type of sensor uses numerous layers in the manufacturing process, has many process steps, and hence increases the production cost.